Subsea Electrical Distribution System Having a Modular Subsea Circuit Breaker and Method for Assembling Same

ABSTRACT

A system and method for coupling electrical power subsea. The system comprises a subsea electrical distribution system having at least one subsea circuit breaker assembly. The subsea circuit breaker assembly comprises a modular subsea busbar assembly configured to receive a plurality of modular cubsea circuit breaker assemblies and at least one modular subsea circuit breaker assembly secured to the modular subsea busbar assembly. The modular subsea circuit breaker assemblies may be coupled by subsea power cables to a source or power, an electrical load, or other subsea circuit breaker assemblies.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional patent application No.61/639,865, filed on Apr. 28, 2012, which is hereby incorporated byreference in its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to subsea electrical systemsand, more specifically, to a subsea electrical distribution systemcomprising a subsea circuit breaker.

2. Description of the Related Art

This section is intended to introduce the reader to aspects of art thatmay be related to aspects of the present invention, which are describedand/or claimed below. This discussion is believed to be helpful inproviding the reader with background information to facilitate a betterunderstanding of the various aspects of the present invention.Accordingly, it should be understood that these statements are to beread in this light, and not as admissions of prior art.

The petroleum industry has seen an increase in interest in the placementof pumping and/or processing equipment for fluids produced from subseawells on the sea floor. Subsea pumping and processing system areparticularly suited for challenging environments, such as the deep seaand Arctic, which are difficult to support from fixed platforms orfloating production units. Subsea hydrocarbon production fields maycomprise many subsea wells extending over hundreds of square miles.Therefore, subsea pumping and/or processing equipment may be required tobe placed at several locations many miles apart.

Power for the subsea pumping and/or processing equipment must besupplied from a fixed platform, a floating production unit, or fromland. Thus, power cables may be needed to cover extreme distances,possibly a hundred miles or more. The greater the number of pumpingand/or processing units in a production field, the greater the number ofpower cables extending over these long distances are needed. Suchsystems are complicated and expensive.

SUMMARY OF THE INVENTION

A system and method for coupling electrical power subsea. The systemcomprises a subsea electrical distribution system having at least onemodular circuit breaker assembly. The modular circuit breaker assemblyis controlled by a control system that has a plurality of circuitbreaker controls. Each circuit breaker is operable to be controlled by aplurality of circuit breaker controls and each circuit breaker controlis operable to control a plurality of circuit breakers. Therefore,control of each circuit breaker is maintained even if a circuit breakercontrol fails. The system has extendable electrical connectors tofacilitate connection of subsea electrical distribution systemcomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1 is a schematic diagram of a subsea system, in accordance withexemplary embodiments of the present techniques;

FIG. 2 is a schematic diagram of a modular subsea electricaldistribution system, in accordance with an exemplary embodiment of thepresent techniques;

FIG. 3 is a schematic diagram of a control and monitoring system for themodular subsea electrical distribution system of FIG. 2, in accordancewith exemplary embodiments of the present techniques;

FIG. 4 is a block diagram of a subsea circuit breaker and redundantcontrol and monitoring equipment for a modular subsea electricaldistribution system, in accordance with exemplary embodiments of thepresent techniques;

FIG. 5 is a schematic diagram of a subsea circuit breaker and redundantcontrol and monitoring equipment for a modular subsea electricaldistribution system, in accordance with exemplary embodiments of thepresent techniques;

FIGS. 6 and 7 are perspective views of a modular subsea circuit breakerassembly for a subsea electrical distribution system, in accordance withexemplary embodiments of the present techniques;

FIG. 8 is a perspective view of a modular subsea circuit breaker for amodular subsea electrical distribution system, in accordance withexemplary embodiments of the present techniques;

FIG. 9 is a perspective view of a modular subsea circuit breakerassembly for a modular subsea electrical distribution system, inaccordance with exemplary embodiments of the present techniques;

FIG. 10 is an elevation view of a modular subsea circuit breakerassembly and a pair of power cable harness assemblies having aretractable/extendable connector for a modular subsea electricaldistribution system, in accordance with exemplary embodiments of thepresent techniques;

FIG. 11 is a perspective view of the power cable harness assembly ofFIG. 10 with the retractable/extendable connector in the retractedposition, in accordance with exemplary embodiments of the presenttechniques;

FIG. 12 is a perspective view of the power cable harness assembly ofFIG. 10 with the retractable/extendable connector in the extendedposition, in accordance with exemplary embodiments of the presenttechniques;

FIG. 13 is a perspective view of the modular subsea circuit breakerassembly of FIG. 10 being removed and lifted from the modular subseaelectrical distribution system, in accordance with exemplary embodimentsof the present techniques;

FIG. 14 is a perspective view of the power cable harness assembly ofFIG. 10 and an electrical load being removed and lifted from the modularsubsea electrical distribution system, in accordance with exemplaryembodiments of the present techniques;

FIG. 15 is a schematic diagram of a subsea modular electricaldistribution system for a sea-based wind farm, in accordance withexemplary embodiments of the present techniques;

FIG. 16 is a simplified schematic diagram of the subsea electricaldistribution system, in accordance with exemplary embodiments of thepresent techniques;

FIG. 17 is an elevation view of a prior art subsea circuit breaker andbus bar enclosure system

FIG. 18 is an elevation view of a modular circuit breaker assembly, inaccordance with exemplary embodiments of the present techniques;

FIG. 19 is an elevation view of a penetrator assembly for a modularcircuit breaker assembly, in accordance with exemplary embodiments ofthe present techniques.

FIG. 20 is a schematic diagram of a subsea system comprising a modularsubsea electrical distribution system, in accordance with an alternativeembodiment of the present techniques;

FIG. 21 is a perspective view of a modular subsea circuit breakerassembly, in accordance with an exemplary embodiment of the presenttechniques; and

FIG. 22 is an elevation view of a modular subsea electrical distributionsystem, in accordance with an alternative embodiment of the presenttechniques.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developers' specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill in the art and having thebenefit of this disclosure.

Referring generally to FIG. 1, a system for providing electric powersubsea is presented and referenced generally by reference numeral 30. Inthe illustrated embodiment, a surface facility 32 provides High voltagealternating current (“HV AC”) electric power and control signals to asubsea electrical distribution system 34 via an umbilical cable 36.There is no set voltage value that defines what is “High voltage”.However, in this embodiment, the voltage of HV AC provided by theumbilical is 110 kV AC or greater. In this embodiment, the surfacefacility 32 is located on land. However, the surface facility 32 mayalso be an off-shore platform or a vessel, such as a floating productionand offloading (“FPO”) vessel. As will be discussed in more detailbelow, the subsea electrical distribution system is a modular systemthat may be assembled in different configurations to meet systemdemands. In the illustrated embodiment, the subsea electricaldistribution system 34 is configured to provide power to a first subseaload 38 and a second subsea load 40. The subsea electrical distributionsystem 34, as well as subsea loads 38, 40 may be located at extremedistances from the surface facility 32. For example, the subseaelectrical distribution system 34 and subsea loads 38, 40 may be 150 kmor more from the surface facility 32. In addition, the subsea electricaldistribution system 34 and subsea loads 38, 40 may be located on anocean floor several thousand feet below the surface of the ocean.Although only two subsea loads 38, 40 are shown in this embodiment, itis envisioned that many more subsea loads would receive power throughthe subsea electrical distribution system 34, rather than receivingpower individually from the surface.

Referring generally to FIG. 2, the subsea electrical distribution system34 is a modular system having a plurality of circuit breaker modulesthat may be connected together to form the system 34. The circuitbreaker modules provide the system 44 with its modularity. The circuitbreaker modules may be assembled and connected in a myriad ofconfigurations to meet the demands of the subsea electrical distributionsystem 34. The circuit breaker modules are provided in the illustratedembodiment to enhance the flexibility and reliability of the subseaelectrical distribution system 44.

In this embodiment, the subsea electrical distribution system 34comprises a pair of central circuit breaker modules 42 that areconfigured to receive power and then distribute the power to a pluralityof remote circuit breaker modules 44. The remote circuit breaker modules44 may be located near the central circuit breaker modules 42 or atgreater distances, such as tens of kilometers away. In this embodiment,the central circuit breaker modules 42 receive power from a first subseaumbilical 46 and a second subsea umbilical 48 for reliability. However,a single subsea umbilical may be used. As will be discussed in moredetail below, the first and second subsea umbilicals 46, 48 comprise HVAC power cables, High voltage direct current (“HV DC”) power cables, andfiber optic communication cables in this embodiment. As above, the HV ACcarried by the umbilicals 46, 48 in this embodiment is 110 kV AC orgreater. However, lower voltages may be provided. As with AC, there isno definitive DC voltage value that defines HV DC. In this embodiment,the HV DC carried by the umbilicals 46, 48 is between 2-10 kV DC.However, greater or lower DC voltages may be provided. The remotecircuit breaker modules 44, in turn, are configured to provide power toa plurality of subsea electric loads 50. In the illustrated embodiment,the power received from the first umbilical 46 and a second umbilical 48are reduced by a pair of subsea step-down transformers 52. However,power may be received at a lower voltage 36 kV), such that subseastep-down transformers are not required.

In this embodiment, the power received by the subsea electricaldistribution system 34 is reduced by a pair of step-down transformers 52before it is transmitted to the central circuit breaker modules 42. Forexample, the subsea transformers 52 may step-down the voltage of the HVAC electrical power from 110 kV AC to 36 kV AC. In this embodiment, thecentral circuit breaker modules 42 of the subsea electrical powerdistribution system 34 comprise a first circuit breaker module 54 and asecond circuit breaker module 56. However, a single central circuitbreaker module 42 may be used, particularly if only one umbilical isused. In this embodiment, the first circuit breaker module 54 receivespower from the first umbilical 46 and the second circuit breaker modulereceives power from the second subsea umbilical 48. The first and secondcircuit breaker modules 54, 56 comprise a plurality of circuit breakersfor selectively supplying electric power. The number of circuit breakersprovided in each circuit breaker module may be varied depending upon thesystem requirements, such as the number of electrical loads to besupplied with power. In the illustrated embodiment, the first and secondcircuit breaker modules 54, 56 each comprise five circuit breakerassemblies 57, 58, 59, 60, 61. One side of each circuit breaker assembly57, 58, 59, 60, 61 is connected to a common bus bar 62 and the otherside of each circuit breaker assembly 57, 58, 59, 60, 61, the “freeside”, may be coupled to a power source or a load depending on thedesired configuration. The first and second circuit breaker modules 54,56 are configured in this embodiment so that the free side of circuitbreaker assembly 57 receives power from one of the subsea umbilicals 46,48. Power passes through circuit breaker assembly 57 to the bus bar 62.Circuit breaker assembly 57 is used to selectively connect anddisconnect the bus bar 62 from power coming from one of the subseaumbilicals 46, 48. The free side of circuit breaker assemblies 58, 59,60, and 61 of the first and second circuit breaker modules 54, 56 areeither coupled to remote circuit breaker modules 44, loads, or notconnected to anything for use as a spare.

The remote circuit breaker modules 44 comprise a third circuit breakermodule 64 that comprises three circuit breaker assemblies 57, 58, 59,rather than five. In this configuration, the third circuit breakermodule 64 is connected to the free side of circuit breaker assembly 58of the first circuit breaker module 54. This enables power to beprovided to the bus bar 62 of the third circuit breaker module 64 fromthe first circuit breaker module 54. The free sides of circuit breakerassemblies 57, 58, 59 of the third circuit breaker module 64 are coupledto loads 50. The three circuit breaker assemblies 57, 58, 59 of thethird circuit breaker module 64, thus, are operable to selectivelyconnect and disconnect the loads 50 and the bus bar 62 of the thirdcircuit breaker module 64.

The remote circuit breaker modules 44 are configured to receive powerfrom either subsea umbilical 46, 48. In this embodiment, the remotecircuit breaker modules 44 also comprise a fourth circuit breaker module66, a fifth circuit breaker module 68, and a sixth circuit breakermodule 70. Circuit breaker assembly 57 of the fourth circuit breakermodule 66 is coupled to circuit breaker assembly 59 of the first circuitbreaker module 54. This enables power to be provided to the bus bar 62of the fourth circuit breaker module 66 from the first subsea umbilical46 via circuit breaker 57 of the fourth circuit breaker module 66. Inaddition, circuit breaker assembly 61 of the fourth circuit breakermodule is connected by a link 72 to circuit breaker assembly 57 of thefifth circuit breaker module 68. Circuit breaker assembly 61 of thefifth circuit breaker module 68 is coupled to circuit breaker assembly59 of the second circuit breaker 58. This enables power to be providedto the bus bar 62 of the fifth circuit breaker module 68 from the secondsubsea umbilical 48 via circuit breaker assembly 61 of the fifth circuitbreaker module 68. Thus, by selectively operating circuit breakerassembly 57 of the fourth circuit breaker module 66 and circuit breakerassembly 61 of the fifth circuit breaker module 68, power may beprovided to bus bars 62 of the fourth and fifth circuit breaker modules66, 68 from either the first subsea umbilical 46 or the second subseaumbilical 48. Alternatively, the sixth circuit breaker module 70 iscoupled to both the first and second circuit breaker modules. Byselectively operating circuit breaker assembly 57 and circuit breakerassembly 61 of the sixth circuit breaker module 70, power may besupplied to the bus bar of the sixth circuit breaker module 70 fromeither the first umbilical 46 or the second umbilical 48 via the firstand second circuit breaker modules 54, 56.

The subsea electrical distribution system 44 may be used to providepower to a variety of loads 50, rather than routing power directly toeach load 50 from the surface. This greatly simplifies powerdistribution. In this embodiment, each of the loads 50 comprises anadditional step-down transformer 76 to supply power to a variable speeddrive (“VSD”) 78. The VSD 78 provides variable speed electric power to amotor 80 to drive a pump 82. Similarly, a load 50 may be a variablefrequency drive (“VFD”). The pumps 82 may be used to pump fluids from asubsea well to a processing unit, for example. However, the VSDs may beused to drive subsea compressors, as well.

Referring generally to FIG. 3, operation of the subsea electricaldistribution system 34 is controlled by a control and monitoring system84. In the illustrated embodiment, a computer system 86 is used toenable a user to manage the subsea electrical distribution system 34 viathe control and monitoring system's HMI (Human Machine Interface). Thecomputer system 86 may be located on-shore or at sea aboard a platformor vessel. The computer 86 may be used to transmit the user's close andopen circuit breaker orders, automatically vary the speed of the VSDs,and perform other control functions. In addition, sensors may be coupledto the computer system 86 to provide the user with information tofacilitate operation of the subsea electrical distribution system 34 andloads 50.

In the illustrated embodiment, the subsea umbilicals 46, 48 also includecommunication lines 88, which enable communication between the computersystem 86, the subsea electrical distribution system 34 and loads 50.Preferably, the communication lines 88 are fiber optic cables routedalong with HV AC and DC power cables in the umbilicals 46, 48. Theumbilicals 46, 48, are terminated at a subsea umbilical terminationassembly (“SUTA”) 90 in this embodiment. From each SUTA 90,communication lines 88 are routed to protection and control modules 92corresponding to each of the circuit breaker modules 54, 56, 64, 66, 68,70. Each of the protection and control modules 92 has an Ethernet switch94 that receives the fiber optic lines 88 in the illustrated embodiment.In the illustrated embodiment, the communication is based on use offunctionality described IEC 61850. Reports are used to transmitinformation to the user for monitoring purposes. Control functions areexecuted by means of Generic Object Oriented Substation Events (GOOSE).GOOSE messages are also used for protection where communication betweenprotection relays is required such as for subsea cables 72, 74. The useof IEC 61850 allows all communication required for protection, controland monitoring to transit via the fiber optic cables installed withinthe umbilicals and subsea cables. This avoids having to installadditional cables for protection, monitoring and control.

In addition, each protection and control module 92 comprises aprotection relay 96 and one or more programmable logic controllerfunctions (PLCs) 98. In addition to the protection functions, theprotection relay 96 also comprises monitoring equipment for the subseaelectrical distribution system 34, such as circuit breaker conditions,and the plurality of loads 50. The PLC functions 98 are used to controlthe circuit breaker assemblies 58, 60. The protection relay 96 isoperable to provide a signal to the PLC functions 98 to trip the circuitbreakers when an undesired condition is reached, such as an overloadcondition. The protection relay provides direct tripping of the circuitbreaker for electrical faults. The Ethernet switch 94 routescommunications between the computer system 86, the protection relay 96,and the PLC functions 98. The PLC functions can be housed in discretepieces of equipment or can be integrated into another electronic devicesuch as a protection relay. The “PLC” function can have differentembodiments.

Referring generally to FIGS. 4 and 5, detailed views of the firstcircuit breaker module 54 and its corresponding protection and controlmodule 92 are presented. Circuit breakers assembly 57 comprises acircuit breaker 102. Similarly, circuit breaker assembly 58 comprises acircuit breaker 104. In the illustrated embodiment, each of the circuitbreakers assemblies 57, 58 is connected to two protection and controlmodules 92 for redundant protection: a first control unit 106 and asecond control unit 108. The first control unit 106 and second controlunit 108 are operable to selectively open and close circuit breakers102, 104. If one control unit 106, 108 fails, the other control unit108, 106 can still selectively open and close both circuit breakers 102,104. Each protection and control module 92 has a main relay and anauxiliary relay function that control the opening and closing of circuitbreakers 102, 104. For example, the first control unit 106 has a mainrelay function 110 and an auxiliary relay function 112. Similarly, thesecond control unit 108 has a main relay function 114 and an auxiliaryrelay function 116. The main relay function of a control unit isconnected to one circuit breaker, while the auxiliary relay function isconnected to a second circuit breaker. For example, main relay function110 of the first control unit 106 is connected to circuit breaker 102and the auxiliary relay 112 is connected to circuit breaker 104.Similarly, circuit breaker 104 is connected to the main relay function110 of control unit 106 and the auxiliary relay function 116 of controlunit 108. If control unit 106 fails, circuit breaker 102 can still becontrolled by auxiliary relay function 116 of control unit 108. In theillustrated embodiment the main relay function and the auxiliary relayfunction are housed in the same piece of equipment, known as a controlunit.

As best illustrated in FIG. 5, circuit breakers are opened and closed byclosing coils and trip coils, respectively. Each circuit breakerassembly has a spring-charged mechanism for opening and closing thecircuit breaker and the circuit breaker closing coils and trip coilscontrol the spring-charged mechanism. If a circuit breaker is open andthe closing coil is energized, the spring-charged mechanism will closethe circuit breaker. Similarly, when the circuit breaker is closed andthe trip coil is energized, the spring-charged mechanism will open thecircuit breaker. In the illustrated embodiment, each circuit breaker hasredundant trip coils and closing coils. Surface circuit breakers haveonly a single closing coil. However, because of the difficulty inremoving a circuit breaker module from subsea if the closing coil wereto fail, two closing coils are provided in each circuit breaker in thisembodiment. Circuit breaker assembly 57 has a first trip coil 118 and afirst closing coil 120 that are connected to the main relay function 110of control unit 106. In addition, circuit breaker assembly 57 has asecond trip coil 122 and a second closing coil 124 that are connected tothe auxiliary relay function 116 of the second control unit 108. Eithertrip coil 118, 122 can open the circuit breaker 102 and either closingcoil 120, 124 can close the circuit breaker 102. A first electric motor126 and a second electric motor 127 having separate power supplies areprovided to energize the spring-charged mechanism 128 when the spring isdischarged. A surface circuit breaker has only a single motor 126.However, because of the difficulty in repairing/replacing a subseacircuit breaker if the motor 126 fails, motors 126, 127 with separatepower supplies are provided for reliability in this embodiment.

Referring generally to FIGS. 4 and 5, the protection and control modules92 also are connected to sensors within the circuit breaker assemblies57, 58. For example, the main relay function 110 of the first controlunit 106 is connected to a first set of phase current sensors 130 and afirst zero-sequence current sensor 132. The auxiliary relay function 114of the second control unit 108 is connected to a second set of phasecurrent sensors 134 and a second zero-sequence current sensor 136.Similarly, the main relay function 114 of the second control unit 108 isconnected to a first set of phase current sensors 138 and a firstzero-sequence current sensor 140 associated with the second circuitbreaker assembly 58. The auxiliary relay function 112 of the firstcontrol unit 106 is connected to a second set of phase current sensors142 and a second zero-sequence current sensor 144 associated with thesecond circuit breaker 58.

Referring generally to FIGS. 6 and 7, an embodiment of a modular subseacircuit breaker assembly 146 for housing a circuit breaker assembly 147for use in the subsea electrical distribution system 34 of FIGS. 1-5 ispresented. The circuit breaker assembly 147 is housed within awater-tight enclosure 148. The enclosure 148 protects the internalcomponents from seawater. One end of the enclosure 148 has a gas sealingbarrier 149 and the other end has a circuit breaker operating mechanismenclosure 150. The circuit breaker operating mechanism enclosure 150 hasa series of connections 151 for connection to the control and monitoringsystem 84. In addition, the enclosure 148 has three sealed openings 152called “penetrators” to which each phase of a three-phase power cablemay be connected for connection to the circuit breaker assembly 147. Inaddition, in this embodiment, the enclosure 148 is filled with sulfurhexafluoride (SF₆) gas to a pressure of two atmospheres for electricalinsulation between the circuit breaker assembly 147 and the enclosure148.

In the illustrated embodiment, the circuit breaker assembly 147 is athree-phase circuit breaker. Each phase of the three-phase power has itsown circuit breaker pole 153. Within each circuit breaker pole 153 isSF₆ gas to quench arcing between contacts when opening and closing thecircuit breakers due to the large voltages utilized in the subseaelectrical distribution system 34. A circuit breaker pole using vacuumfor arc quenching can also be used. External electrical power cables areconnected to the penetrators 152 on the enclosure 148 for internalconnection to three terminals 154 on the circuit breaker assembly 147.Each circuit breaker pole 153 has a conductor 155 that extends throughthe gas sealing barrier 149 of the enclosure 148 into a bus barcompartment to which the modular circuit breaker assembly 146 issecured.

Referring generally to FIG. 8, an embodiment of the first circuitbreaker module 54 is presented. In this embodiment, the first circuitbreaker module 54 comprises five modular circuit breaker assemblies 146connected to a bus bar assembly 162 housing the bus bar 59 (not shown).The bus bar assembly 162 is comprised of two end assemblies 164connected to a central assembly 166. However, additional centralassemblies 164 may be connected together to extend the bus bar assembly162. The interior of the bus bar assembly 162 is insulated with SF₆ gasin this embodiment. As will be discussed in more detail below, the useof SF₆ gas for insulation, rather than oil, enables a smaller bus barassembly 162 to be used, as well as requiring fewer penetrations throughbarriers that have to withstand differential pressure. Each of themodular circuit breaker assemblies 146 has a connector 168 forconnecting to a power cable. Each of the connectors 168 is connected toa penetrator 152 which seals the opening in the enclosure 148.

In the illustrated embodiment, the first circuit breaker module 54comprises a first modular circuit breaker assembly 170, a second modularcircuit breaker assembly 172, a third modular circuit breaker assembly174, a fourth modular circuit breaker assembly 176, and a fifth modularcircuit breaker assembly 178. In this embodiment, circuit breaker 57(not shown) is housed within the first modular circuit breaker assembly170. Circuit breaker 58 (not shown) is housed within the second modularcircuit breaker assembly 172. Circuit breaker 59 (not shown) is housedwithin the third modular circuit breaker assembly 174. Circuit breaker60 (not shown) is housed within the fourth modular circuit breakerassembly 174. Finally, circuit breaker 61 (not shown) is housed withinthe fifth modular circuit breaker assembly 176. Opposite the thirdmodular circuit breaker assembly 174 is a spare space for an additionalmodular circuit breaker assembly. This would bring the total number ofcircuit breakers to six if this spare space was used.

Referring generally to FIG. 9, the first circuit breaker module 54 ishoused within a supporting structure 180 in the illustrated embodiment.The supporting structure 180 comprises a frame 182 in which the firstcircuit breaker module 54 is supported. In addition, the supportingstructure 180 is adapted to route power to and from each of the modularcircuit breaker assemblies 146 of the first circuit breaker module 54.The first circuit breaker module 54 is configured by routing powereither to or from each modular circuit breaker assembly 146. Connectorassemblies 184 are disposed around the frame 182. The supportingstructure 180 also comprises a plurality of power cables 186 that extendbetween the connector assemblies 184 and the connectors 168 on thecircuit breaker assemblies 170, 172, 174, 176, 178 to route power to andfrom the modular circuit breaker assemblies 170, 172, 174, 176, 178.Each connector assembly 184 is configured with three wet mate powerconnectors 188 together with alignment guides 190. The alignment guides190 align the power connectors 188 with a corresponding external wetmate connector assembly (not shown). Each power cable 186 is routedbetween a wet mate power connector 188 and a wet mate connector 168 on acircuit breaker assembly 170, 172, 174, 176, 178 in this embodiment. Inaddition, the supporting structure 180 has a plurality of guides 191 foralignment purposes. A cable clamp 192 is mounted on the circuit breakermodule to support the cable at its connection 168. The clamp 192 isdesigned to securely hold the cable at varying external pressures fromsea level to the final installation depth under water.

Referring generally to FIGS. 10-12, in the illustrated embodiment, eachcircuit breaker assembly 170, 172, 174, 176, 178 is connected to anexternal component of the subsea electrical distribution network via asubsea cable 208 by connecting a cable harness assembly 200 having a setof wet mate connectors 202 that may be extended and retracted to thatmodular circuit breaker assembly's connector assembly 184. The connector202 of FIG. 11 and the left side of FIG. 10 is shown in the retractedposition. The connector 202 of FIG. 12 and the right side of FIG. 10 isshown in the extended position. In this embodiment, the cable harnessassembly 200 also comprises a frame 204, and a cable harness 206 forsecuring power cables 208 to the cable harness assembly 200. The frame204 has a plurality of guides 209 for alignment purposes.

To connect the power cables 208 of the cable harness assembly 200 to thecircuit breaker module assembly 180, the frame 204 of the cable harnessassembly 200 is disposed adjacent to the frame 182 of the circuitbreaker module assembly 180 so that the connector 202 is generallyaligned with, and proximate to, the connector assembly 184. In thisembodiment, the frame 182 of the circuit breaker module assembly 180 andthe frames 204 of the cable harness assemblies 200 are disposed on atemplate 210. The template 210 has guideposts (not shown) configured toreceive the guides 191 in the frame 182 of the supporting structure 180and the guides 209 of the cable harness assemblies 200 so that the cableharness assemblies 200 and supporting structure 180 are in properalignment. Each cable harness assembly is independent of the frame 182and all other cable harnesses.

An ROV (not shown) is used to extend the connector 202 towards theconnector assembly 184 of the circuit breaker module 180 to make theconnection. The cable harness assemblies 200 have a connector guideassembly 211 comprising a fixed portion 212 secured to the frame 204 anda movable portion 213 secured to the power cables 208. The ROV (notshown) may secure to the frame 204 and grab the movable portion 213 andeither pull or push the movable portion 213, and power cables 208,relative to the frame to retract or extend the connectors 202. As theconnector 200 is extended, guide pins 214 on the connector 200 engagethe guides 190 on the connector assembly 184 of the circuit breakermodule assembly 180. The engagement between the guide pins 214 and theguides 190 brings the wet mate connectors 214 of the connector 200 intoalignment with wet mate connectors 188 of the first circuit breakermodule 54. Eventually, as the connector 202 is extended, the connectors214 of the connector 202 of the cable harness assembly 200 connect tothe connectors 188 of the first circuit breaker module assembly 54,electrically coupling the power cables 208 to the cables 186 of thesupporting structure 180 of the first circuit breaker module assembly54. Similarly, to disconnect the power cables 208 of the cable harnessassembly 200 from the circuit breaker module assembly 180, an ROV (notshown) is used to retract the connector 202 to disengage from theconnector assembly 184 of the supporting structure 180 of the firstcircuit breaker module 54.

Referring generally to FIG. 13, because the cable harness assemblies 200are selectively connectable to the supporting structure 180, a circuitbreaker module assembly 180 may be removed from the subsea electricaldistribution system 34 for repair/modification without requiring removalof loads 50 or other cables 208 routed to and from the circuit breakermodules. In this view, the circuit breaker module and supportingstructure 180 are guided into and out of position by an ROV 219 on tothe template 210. In addition, the cable harness assemblies 200 may bedisconnected to facilitate fault detection. For example, after aconnector 202 has been disconnected, an ROV may connect to theconnectors 202 to perform test to identify if a fault exists in thepower cable 208 or if the fault exists in the circuit breaker module 54.Alternatively, the ROV can check power cable electrical characteristics.

Referring generally to FIG. 14, similarly, a cable harness assembly 200and connected cable 208 (not shown) may be removed from the subseaelectrical distribution system 34 for repair/modification withoutrequiring removal of the first circuit breaker module assembly 54 orother cables 208 routed to and from the circuit breaker module. Toremove a cable harness assembly 200 from the subsea electricaldistribution system 34, the retractable/extendable connector 202 for itscable harness assembly 200 is retracted; this disconnects the cableharness assembly 200 and connected cable 208 from the circuit breakermodule assembly 180. The cable harness assembly 200, and the cables 208connected to the cable harness assembly 200 may then be raised to thesurface for repair/modification. The cable harness assembly 200 isguided into and out of position by the ROV onto the template 210. If theload 50 remains connected to the cable 208 then it may be raised to thesurface for repair/modification together with the cable harness assembly200 and connected cable 208.

Referring generally to FIG. 15, a wind farm 250 having a modular subseaelectrical distribution network 252 is presented. In the illustratedembodiment, the wind farm 250 comprises a plurality of windturbine-generators 254. In this embodiment, groups 256 of windturbine-generators 254 are electrically connected to a “local” modularsubsea circuit breaker assembly 258. The modular subsea circuit breakerassemblies 258 have the features and characteristics as described abovein respect to FIGS. 2-14, as described above. In this embodiment, eachwind turbine-generator 254 is connected to a corresponding circuitbreaker 260 within a modular subsea circuit breaker assembly 258. Inturn, groups 262 of modular subsea circuit breaker assemblies 258 areconnected to a “regional” modular subsea circuit breaker assembly 264.The “regional” modular subsea circuit breaker assemblies 264 areconnected to a “central hub” modular subsea circuit breaker assembly266. The “central hub” modular subsea circuit breaker assembly 266 isconnected to a step-up transformer 268 to increase the voltage of thepower generated by the wind turbine-generators 254 to a high-voltage fortransmission over a subsea umbilical 270 to a shore facility 272.

Referring generally to FIG. 16, in addition to HV AC power andcommunications lines, the subsea electric system 30 also couples HV DCto, and through, the subsea power distribution system 34. In thisembodiment, HV DC is typically between 2 kV and 10 kV. Previously, HV DCwas coupled to subsea loads in either a separate umbilical or producedsubsea from HV AC transmitted subsea via an umbilical. However, in theillustrated embodiment, the first umbilical 46 is configured with HV ACpower cables, HV DC power cables, and fiber optic cables forcommunication. At the SUTA 90, HV AC power is coupled from the umbilical46 to provide power to loads 50 via a HV AC power cable 300. Inaddition, HV DC power is coupled from the umbilical 46 to a protectionand control module 92 by a HV DC power cable 301. Finally, communicationcapability is coupled from the umbilical 46 to the protection andcontrol module 92 by a fiber optic cable 302. Communication capabilityis provided to process equipment 303 from the protection and controlmodules 92 via a fiber optic cable 302 and a subsea communicationinterface 304. In addition, the protection and control module 92provides DC auxiliary power to the process equipment via an auxiliary DCpower cable 305.

Referring generally to FIG. 17, a representative subsea breaker and busbar assembly is disclosed, and represented generally by referencenumeral 310. The illustrated assembly 310 has a first circuit breaker312 and a second circuit breaker 314. The first circuit breaker 312 hasan enclosure 316 and the second circuit breaker 314 has an enclosure318. The interiors of both enclosures 316, 318 is pressurized with SF₆gas 320. The pressure of the gas 320 may be near atmospheric pressure.Therefore, there will be a large differential pressure between theinterior of the enclosures 316, 318 and the seawater 322 pressuresurrounding the assembly 310 when the assembly 310 is located subsea.The assembly 310 also comprises a bus bar 324 housed within a two-stagepressure compensation housing 325. The bus bar 324 is housed within afirst enclosure 326. The first enclosure 326, in turn, is housed withina second enclosure 328. The first enclosure 326 is filled with a firstoil 330 and the second enclosure 328 is filled with a second oil 332.The viscosities of the oils 330, 332 may vary. The pressure compensationreduces, if not eliminates, the pressure differential between theinterior of the first enclosure 326 and seawater 322. However, itproduces a pressure differential between the oil 330 within the interiorof the first enclosure 326 and the SF₆ gas 320 within the interior ofthe circuit breaker enclosures 316, 318, which may lead to leaks of oilinto the interior of the circuit breaker enclosures 316, 318. Inaddition, this requires two sealed penetrations, a first penetration 334and a second penetration 336, to connect to the bus bar 324, creatingpotential leak paths.

Referring generally to FIG. 18, a simplified drawing of circuit breakermodule 54 of FIG. 8 is presented. In this embodiment, rather thanpressure compensating the interior 338 of the bus bar assembly 162 toseawater pressure, the interior 338 of the bus bar assembly 162 ispressurized with SF₆ gas 320 to a pressure of two atmospheres. The SF₆gas 320 is a better electrical insulator than oil 330, 332. Therefore,the interior 338 of the bus bar assembly 162 requires less volume forelectrical insulation between the bus bar 62 and the enclosure 340 ofthe bus bar assembly 162. Thus, the size of the enclosure 340 may bereduced. In addition, the differential pressure between the gas-filledinterior 338 of the bus bar assembly 162 and the gas-filled interior 342of the circuit breakers assemblies 168, 170 is reduced, if noteliminated, reducing potential for leaks between the bus bar assembly162 and the circuit breaker assemblies 168, 170. This also reduces thenumber of sealed penetrations 344 needed between the bus bar 62 and acircuit breaker 57, 58 by one, reducing potential leak paths.

Referring generally to FIG. 19, an embodiment of a penetrator 344 ispresented. In this embodiment, a conductor 155 from a circuit breaker57, 58, etc., extends through an opening 346 in the pressure barrier 149between the interior and exterior gas or fluids at various pressureratings. In this embodiment, the penetrator 344 comprises insulation 348surrounding the conductor 155 and a body 350 that completes the sealagainst the opening 346 in the pressure barrier 149. The body 350 alsocomprises a boot 352. In this embodiment, the boot 352 also comprises afirst current sensor 354 and a second current sensor 356 integrated intothe boot 352. The current sensors 354, 356 comprise a sensor core 358, asensor winding 360, and sensor insulation 362. The current sensors 354,356 may be current transformers.

Referring generally to FIG. 20, a subsea system is presented andrepresented generally by reference numeral 400. In this embodiment, thesubsea system 400 comprises a modular subsea electrical distributionsystem 402 operable to provide HV AC, Low voltage alternating current(“LV AC”), HV DC, Low voltage direct current (“LV DC”), and fiber opticcommunication lines to power and control subsea loads.

In the illustrated embodiment, a HV AC power cable 300, a HV DC powercable 301, and a fiber optic communication line 302 are coupled to amodular HV Subsea Substation (“HVSS”) 404 comprising a circuit breakermodule 406 and a protection and control module 408. The HV AC powercable 300 is coupled to the subsea circuit breaker module 406. Thesubsea circuit breaker module 406 comprises circuit breaker assemblies57, 58, 59, 60, 61, and a busbar assembly 62, as described above in FIG.2. The HV DC power cable 301 and fiber optic communication line 302 arecoupled to a control and monitoring module 408. In this embodiment, thecontrol and monitoring module 408 comprises a HV DC power and fiberoptic communication line interface 410. DC power and communicationsignals are coupled to a protection and control module 412. Theprotection and control module 412 is, in turn, coupled to the circuitbreaker module 406. The protection and control module 412 is similar toprotection and control module 92 described above in FIGS. 3-5.

In this embodiment, the subsea electrical distribution system 402comprises a LV subsea distribution (“LVSD”) module 414 operable tosupply LV AC power to various loads from the HV AC power and/or the HVDC power supplied by the umbilical 46. HV AC power from the HVSS iscoupled to a subsea transformer 416 via circuit breaker assembly 61. Thetransformer 416 steps-down the HV AC from approximately 33 kVAC toapproximately 690 VAC, which is coupled to the LVSD module 414. Theillustrated embodiment of the LVSD module 410 comprises a first busbarassembly 418 and a second busbar assembly 420 coupled together by across-connect circuit breaker assembly 422. LV AC power from thetransformer 416 is coupled to the first busbar assembly 418 by a firstinlet circuit breaker assembly 424. LV AC power is supplied to thesecond busbar assembly 420 from an uninterruptable power supply (“UPS”)module 426 through a circuit breaker assembly 428 in the LVSD module414. The UPS receives HV DC power and fiber optic communication linesfrom the HV DC power and fiber optic communication line interface 410.In addition, in the illustrated embodiment, the UPS module 426 comprisesan emergency battery 430 operable to provide emergency DC power if powerfrom the umbilical 46 is lost. The UPS module 426 comprises a DC to ACpower supply 432 that converts DC power from either the umbilical 46,via the communication and monitoring module 408, or the emergencybattery 430 to LV AC. In addition, the UPS module 426 comprises a DC toDC power supply 434 for providing DC power to loads from eitherumbilical, via the communication and monitoring module 408, or theemergency battery 430

The LVSD module 414 comprises a plurality of circuit breaker assemblies436. Some of the circuit breaker assemblies are coupled to the firstbusbar assembly 418 and some are coupled to the second busbar assembly420. Depending upon the position of the cross-connect circuit breakerassembly 422, power may be supplied to the circuit breaker assemblies436 from the HVSS 404 and/or the UPS module 426. In this embodiment, thepower supplied by the UPS module 426 is considered as “Secure Power”meaning that it is available when the normal AC power has failed. Inthis embodiment, during normal operation, the cross-connect circuitassembly 422 is open and circuit breaker assembly 428 is closed so thatthe circuit breaker assemblies are supplied power by the HVSS 404 andthe UPS 432. However, when there is a loss of power from the UPS module432, the cross-connect 422 is closed and circuit breaker assembly 428 isopened so that the AC power from the HVSS 404/umbilical 46 may supplypower to critical loads that must remain energized. In this embodiment,each circuit breaker assembly 436 couples power to subsea loads via anisolation transformer 438. The outgoing circuits of the LVSD module 426are provided with isolation transformers 438 in order to allow loads tocontinue to be supplied should an earth fault occur on the load side ofthe isolation transformer 438.

The monitoring and control of the devices within the LVSD module 414 isperformed via fiber optic cables 302 connected to the CMM 408. Inaddition, sensors installed on the step-down transformer 416 areconnected to the LVSD module via subsea cable 440. The LVSD module 414converts signals from these sensors to optical signals for transmissionvia the fiber optic cables 302 connecting the LVSD module 414 to the CMM408 and, thus, to other subsea equipment and the shore station.

The subsea system 400 also comprises a subsea heating system 442. Thesubsea electrical distribution system 402 comprises a heat tracingmodule (“HTM”) 444 for supplying LV AC power to the heating system 442.The HTM 444 is a LV AC switchgear module dedicated to the subsea heatingsystem 442. High power subsea heating circuits 446 used for initialheating are supplied by the HVSS 404 via a power cable 450 coupled tothe first busbar 418 of the LVSD module 414. Lower power circuits 448used for maintaining a temperature are supplied by a power cable 452coupled to the second busbar 420 of the LVSD module 414 and, therefore,may be supplied by the UPS module 426 if power from the HVSS 404 islost. The HTM 444 also comprises a plurality of isolation transformers454. The isolation transformers 454 in the HTM 444 are used for twopurposes. The first purpose is to allow continued operation in case ofan earth fault on the load side of the transformer 454. The otherpurpose is to adapt the output voltage to that required by the heatingsystem 442. For example, the heating system 442 may require voltages ofgreater than 1000 V AC. This second purpose may be a new idea for asubsea heating power supply. The LVSD module 414 also communicates withthe HTM 442 via fiber optic cables 302. This allows the HTM 444 to bemonitored and remotely controlled in the same manner as the LVSD module414. Similarly any sensors in the heating system 442 can be connected todevices within the HTM 444 and converted to optical signals fortransmission to other subsea equipment or to the shore station.

LV AC also is supplied to a VFD assembly 456 in this embodiment. The VFDassembly 456 receives main HV AC power form the HVSS 404. In theillustrated embodiment, LV AC from the first busbar 418 of the LVSDmodule 414 is provided to the VFD assembly 456 to power a pre-charge andpre-magnetization transformer 458 located within the VFD assembly 456.This transformer 458 must be energized before main AC power from theHVSS is energized. In previous subsea VFD systems, power to a pre-chargeand pre-magnetization transformer of a VFD was provided from a subsea ortopside UPS. In this embodiment, only normal AC power is required, notsecure power. LV AC power from the HVSS 404 via the first busbar 418 isprovided to secondary functions 460. Secure power from the second busbar420 is provided to primary functions 462, such as the controlelectronics of the VFD and for cooling fans, if provided. A power cable464 is provided to couple LV AC power from the first busbar 418 to thesecondary functions and a separate power cable 466 is provided to couplesecure LV AC power from the second busbar 420 to the main functions 462.

The subsea system 400 also comprises a magnetic bearing module (“MBM”)480, which supplies power to a magnetic bearing 482 for a rotatingdevice. The VFD 456 is used to power an electric motor 80, which, inturn, may be used to drive a number of different rotating devices, suchas a subsea pump 483 or subsea compressor 484. The subsea pump 483 maybe used to pump production fluids from a subsea well to a platform,vessel, or shore facility. The subsea compressor 484 may be used tocompress production gases from a subsea well, which may be piped to aplatform, vessel, or shore facility. The magnetic bearing 482 providessupport for the rotating shafts of the rotating devices powered by theVFD 456. In this embodiment, the MBM 480 may receive DC power from theUPS module 426 or LV AC from the LVSD module 414. A DC power cable 486couples DC power from the UPS module 426 to the MBM 480. An AC powercable 488 couples AC power from the LVSD module 414 to the MBM 480.

In the illustrated embodiment, the subsea system 400 comprises a subseacontrol module (“SCM”) 500. The SCM 500 controls the subsea productionand processing equipment. In this embodiment, the SCM 500 comprises asubsea electrical module (“SEM”) 502. In previous designs, the SCM 500and its embodied SEM 502 received power directly from a shore facilityvia a separate power cable. In this embodiment, main function controller504 of the SEM 502 receives secure power from the second busbar 420 ofthe LVSD module 414. Secondary function controller 506 receives powerfrom the first busbar 418 of the LVSD module 414. As noted above, securepower from the second busbar 420 of the LVSD module 414 may be LV ACpower stepped-down from the HV AC power of the umbilical 46 or AC powerconverted either from the HV DC power in the umbilical 46 or emergencybattery 430 in the UPS module 426. A power cable 510 is provided tocouple LV AC power from the first busbar 418 to the secondary functioncontroller 506 and a separate power cable 512 is provided to couplesecure LV AC power from the second busbar 420 to the main functioncontroller 504.

In addition, the subsea electrical distribution system 402 providespower to motor-operated valves and actuators, represented generally byreference numeral 520. One or more of the motor-operated valves andactuators 520 may be powered by LV AC from the first busbar 418 of theHVSS 414. In addition, one or more of the motor-operated valves andactuators 520 may be powered by secure power from the second busbar 420of the LVSD module 414. Secure power may be LV AC power stepped-downfrom the HV AC power of the umbilical 46 or AC power converted eitherfrom the HV DC power in the umbilical 46 or emergency battery 430 in theUPS module 426. A power cable 522 is provided to couple LV AC power fromthe first busbar 418 to the motor-operated valves and actuators 520 anda separate power cable 524 is provided to couple secure LV AC power fromthe second busbar 420 to the motor-operated valves and actuators 520.

In addition, in this embodiment, the subsea electrical distributionsystem 402 provides power to a subsea tree 530 via a power cable 532.The subsea tree 530 monitors and controls the production of fluids froma subsea well. The subsea tree 530 is secured to a subsea wellhead (notshown) of a completed subsea well. The subsea tree 530 has valves thatcontrol the flow of fluids flowing from the subsea well or gas or waterinjected into the subsea well. In this embodiment, the valvescontrolling flow to, from, and through the subsea tree 530 are operatedusing electric operators powered from the power cable 532 of the subseaelectrical distribution system 402. However, the electric operators maybe powered with DC power from the DC module 426. In addition, a fiberoptic cable 302 is routed to the subsea tree 530 to enable the subseatree 530 to be controlled from the surface.

Referring generally to FIG. 21, an embodiment of a modular subseacircuit breaker assembly for use with the subsea electrical distributionsystem described above is presented and represented generally byreference numeral 700. In this embodiment, a subsea circuit breakerassembly 702, such as one of the circuit breaker assemblies 54, 56, 64,66, 68, 70 of FIG. 2, is supported by a frame 704. In addition, aprotection and control module 706, such as protection and control module92 of FIG. 3, is supported by a frame 708. The protection and controlmodule 706 may be connected to the circuit breaker assembly 702 bydisposing the protection and control module 706 and frame 708 proximateto the circuit breaker assembly 702 and frame 704 and connecting cablesbetween the protection and control module 706 and the circuit breakerassembly 702. Either the protection and control module 706 or circuitbreaker assembly 702 may be replaced by disconnecting the cablesconnecting them together and lifting the device to be replaced to thesurface. A replacement device may be lowered to the position of theoriginal device and the electrical cable re-connected. Subsea cables andflying leads are connected and disconnected by means of an ROV (notshown).

Referring generally to FIG. 22, an alternative embodiment of a modularsubsea electrical distribution system 800 is presented. As above, thebusbar assembly 800 comprises a busbar 802 housed within a sealedhousing 804. Also as above, the housing 804 is pressurized with SF₆ gas.However, in this embodiment, an input electrical power cable 806 isconnected directly to the busbar 802, rather than to a supply-sidecircuit breaker, such as circuit breaker 57 in FIG. 2. The cable 806extends through a sealed penetration 808 in the housing 804. The end ofthe cable 806 opposite the busbar 802 is connected to an electricalconnector 810. Circuit breaker assemblies may be connected to the busbar802 to couple power from the busbar 802 to electrical loads.Alternatively, additional electrical cables 806 may be connecteddirectly to the busbar 802 and routed to supply electrical loads. Thebusbar housing 804, cable 806, cable electrical connector 810, etc., aresupported by a frame 812.

As noted above, one or more specific embodiments of the presentinvention were provided above. In an effort to provide a concisedescription of these embodiments, not all features of an actualimplementation were described in the specification. It should beappreciated that in the development of any such actual implementation,as in any engineering or design project, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which may vary from one implementation toanother. Moreover, it should be appreciated that such a developmenteffort might be complex and time consuming, but would nevertheless be aroutine undertaking of design, fabrication, and manufacture for those ofordinary skill in the art and having the benefit of this disclosure.

What is claimed is:
 1. A subsea electrical distribution system,comprising: a first subsea circuit breaker module comprising a firstbusbar and a first plurality of circuit breakers electrically coupled tothe first busbar; and a second subsea circuit breaker module comprisinga second busbar and a second plurality of circuit breakers connected tothe second busbar, wherein the second busbar is electrically coupled tothe first busbar of the first subsea circuit breaker module.
 2. Thesubsea electrical distribution system of claim 1, comprising a firstsubsea circuit breaker control module disposed in an enclosure separatefrom the first circuit breaker module, wherein the first subsea circuitbreaker control module is in communication with the first subsea circuitbreaker module, the first subsea circuit beaker control module beingoperable to control opening and closing of the plurality of circuitbreakers within the first subsea circuit breaker module.
 3. The subseaelectrical distribution system of claim 2, wherein at least one circuitbreaker of the first plurality of circuit breakers comprises a closingcoil and a trip coil, each of the closing coil and the trip coil beingcontrolled by the first subsea circuit breaker control module.
 4. Thesubsea electrical distribution system of claim 2, wherein the firstsubsea circuit breaker module is in communication with a surfacelocation via a fiber optic communication link.
 5. The subsea electricaldistribution system of claim 1, wherein the second busbar iselectrically coupled to the first busbar through a first circuit breakerin the first plurality of circuit breakers.
 6. The subsea electricaldistribution system of claim 5, wherein the second busbar iselectrically coupled to the first busbar through a first circuit breakerin the second plurality of circuit breakers.
 7. The subsea electricaldistribution system of claim 1, comprising a third subsea circuitbreaker module comprising a third busbar and a third plurality ofcircuit breakers connected to the third busbar, wherein the third busbaris electrically coupled to the first busbar of the first subsea circuitbreaker module.
 8. The subsea electrical distribution system of claim 7,wherein the third busbar is electrically coupled to the first busbarthrough a second circuit breaker in the first plurality of circuitbreakers.
 9. A modular subsea circuit breaker assembly, comprising: abusbar enclosure having a hollow interior housing a busbar, wherein thebusbar enclosure comprises a plurality of flanged connections; and aplurality of circuit breaker enclosures, each of the plurality ofcircuit breaker enclosures having a hollow interior housing a circuitbreaker electrically coupled to the busbar, wherein each circuit breakerenclosure comprises a flanged connection securable to a flangedconnection of the busbar enclosure.
 10. The modular subsea circuitbreaker assembly of claim 9, wherein each circuit breaker iselectrically coupled to the busbar by extending a conductor through asealed opening between the busbar enclosure and the circuit breakerenclosure of the circuit breaker.
 11. The modular subsea circuit breakerassembly of claim 10, wherein the quantity of circuit breaker enclosuresin the plurality of circuit breaker enclosures is less than the quantityof flanged connections in the plurality of flanged connections of thebusbar enclosure, further wherein a cover is disposed over any flangedconnections of the busbar enclosure that are not used to secure acircuit breaker enclosure to the busbar enclosure.
 12. The modularsubsea circuit beaker assembly of claim 9, wherein each of the pluralityof flanged connections of the busbar enclosure are oriented so that eachof the plurality of circuit breaker enclosures is oriented transverse tothe busbar.
 13. The modular subsea circuit breaker assembly of claim 12,wherein at least two of the plurality of flanged connections of thebusbar enclosure are oriented on opposite sides of the busbar enclosure.14. The modular subsea circuit breaker assembly of claim 9, comprising acontrol module operable to control opening and closing of at least oneof the plurality of circuit breakers, wherein the control module ishoused in an enclosure separate from the busbar enclosure and each ofthe plurality of circuit breaker enclosures.
 15. A method for assemblinga subsea electrical distribution system, comprising: identifying aquantity of circuit breakers desired in a subsea circuit breakerassembly; securing the quantity of modular subsea circuit breakerassemblies to a modular busbar enclosure having a busbar and a pluralityof connectors configured to receive a modular subsea circuit breakerassembly; and sealing any connectors on the modular busbar enclosure towhich a modular subsea circuit breaker assembly is not secured.
 16. Themethod of claim 15, comprising: coupling a circuit breaker within acircuit breaker assembly to the busbar in the busbar enclosure; andsealing the busbar enclosure from the circuit breaker assembly.
 17. Themethod of claim 15, comprising: securing the modular busbar and theplurality of circuit breaker assemblies to a frame having a plurality ofelectrical connectors secured thereto; connecting a first end of asubsea power cable to a subsea circuit breaker assembly; and connectingan opposite end of the subsea power cable to an electrical connectorsecured to the frame.
 18. A method for assembling a subsea electricaldistribution system, comprising: identifying a quantity of circuitbreakers desired in a subsea circuit breaker assembly; providing aquantity of modular subsea circuit breaker assemblies comprising aquantity of circuit breakers equal to the quantity of circuit breakersdesired in the subsea circuit breaker assembly, each modular subseacircuit breaker assembly having a flanged connector; and securing thequantity of modular subsea circuit breaker assemblies to a modularbusbar enclosure having a busbar and plurality of flanged connectorsconfigured to receive a flanged connector of a modular subsea circuitbreaker assembly.
 19. The method of claim 18, comprising: securing acover to a flanged connector of the busbar enclosure not having amodular subsea circuit breaker assembly secured thereto.
 20. The methodof claim 18, comprising: coupling a circuit breaker within a modularcircuit breaker assembly to the busbar in the busbar enclosure; andsealing the modular busbar enclosure from the modular circuit breakerassembly.